1. Field of the Invention
The present invention relates to an apparatus for visual acuity test, in particular to an apparatus for visual acuity test provided with plural kinds of test charts, for instance, Landolt ring charts, character chart and others.
2. Description of Related Art
In conventional apparatuses for testing visual acuity of an examinee's eye by presenting test charts to the examinee, there is known an apparatus utilizing a method in which the test charts, being printed on semitransparent plates and others, are illuminated one by one from the back of the semitransparent plate by a lamp and the like so that a test chart to be read by the examinee is identified. In such an apparatus for visual acuity testing, the test charts are individually presented to the examinee as above, and besides, a plurality of test charts each for the different visual acuity value or test charts for the same visual acuity value can be synchronously presented. Consequently, the time for testing visual acuity can be shortened.
In addition, there is also an apparatus for visual acuity test in which different kinds of test charts can be utilized by exchanging test chart plates, for instance, from a test chart plate provided with Landolt rings thereon to another test chart plate provided with character charts thereon.
Another apparatus for testing visual acuity has been also proposed in Japanese Laid-Open Utility Model No. SHO 59-19107, in which visual test charts are presented to the examinee by utilizing an electro-optical effect such as liquid crystal and the like.
However, in the former apparatus in which test charts are illuminated from the back of the semitransparent plate by a lamp, presenting various kinds of test charts, such as Landolt rings and character test charts and others, one needs to exchange test chart plates according to the sort of test chart to be used. However, it is troublesome and difficult to exchange test chart plates in testing the visual acuity of an examinee's eye.
In the latter kind of testing apparatus utilizing the liquid crystal, there is not practicable apparatus ensuring the standard testing distance between the apparatus and the examinee; 3 meter (m) or 5 meter (m). The reason is that, in order to display various test charts for a testing distance of 5 m on a liquid crystal plate at actual distance, it is necessary to have a large liquid crystal display area and therefore such apparatus can not be actualized economically and technically.